Uses of stable carbon isotope compositions of organic carbon in sedimentological studies on tropical marine systems

Abstract

Nearshore gradients in the stable isotope composition of sedimentary organic carbon have been repeatedly demonstrated over the past 20 years. Early investigators reasoned that these gradients were due to a mixing of land and marine derived organic matter which retained the mean signatures of their plant precursors, thought to be about −27 and −20% versus PDB, respectively. Although this simple model is still generally applicable, several dichotomies, discovered since the earliest studies, in the fractionation of stable carbon isotopes during marine and land plant photosynthesis have, on the one hand, introduced complications in the interpretation of natural variations but, on the other hand, have made possible a broader usage of carbon isotope signatures. Case histories are presented to illustrate the widened application of stable carbon isotope compositions for: (i) sources and cycling of organic matter in modern tropical marine depositional environments; (ii) contamination of marine sediments by anthropogenic organic residues.